1. Field of the Invention
The present invention relates to a communication apparatus such as a facsimile apparatus capable of communication using a DIS signal having a variable length FIF.
2. Related Background Art
In a conventional facsimile apparatus, a facsimile information field (FIF) of a DIS signal has a constant number of bytes, which signal is sent to a transmission side apparatus in order to notify a capability of a reception side apparatus.
FIF of the DIS signal had 4 bytes several years before, and has increased recently to 10 bytes. A facsimile apparatus shipped around 1985 was not designed to use a DIS signal having 10 bytes of FIF so that if this DIS signal is sent, a communication error occurs.
A facsimile apparatus capable of V. 8 or V. 34 communication, formally recommended by ITU-T in 1996 can receive as a DIS signal having 10 bytes of FIF. However, since a G3 facsimile apparatus manufactured in the first half of 1980""s was recommended by ITU-T, FIF of a DIS signal was permitted up to 4 bytes. Therefore, the apparatus of that period can receive only a DIS signal having 4 bytes or smaller of FIF unless the apparatus was designed to expand FIF. As a fact, the V. 8, V. 34 facsimile apparatus cannot communicate with such an old type of facsimile apparatus.
It is an object of the present invention to provide reliable communication between new and old communication apparatuses having different byte numbers of FIF of a DIS signal.